The present invention relates to a target assembly and its method of use in depositing a layer of material having relatively thin and relatively thick portions adjacent to each other, with a very narrow transition region therebetween. More particularly, the present invention relates to an apparatus and method useful in forming a protective overcoat on a magnetic or magneto-optical recording/information storage/read-out disk, where the thickness of the overcoat layer in an annularly-shaped inner landing, or CSS, zone of the disk is greater than the thickness of the overcoat layer in an outer, data zone of the disk. The present invention also relates to the formation of coatings, such as optical, anti-friction, wear or corrosion-resistant coatings, which require variation of the properties thereof in a radial direction.
Magnetic and magneto-optical (MO) recording media typically require an overcoat for wear and corrosion protection, inasmuch as contact start/stop (CSS) failures in hard disk drives can result in unrecoverable data loss. As a consequence, good tribological performance is one of the most stringent requirements for hard disk drives. Various overcoat materials have been developed for use in the manufacture of hard disk drives, including carbon (C), silicon (Si), and zirconium (Zr)-based materials. Of these, carbon-based overcoats have become widely utilized as a standard protective material in the hard disk industry. Various types of carbon-based overcoats, with and without various dopants, such as hydrogen (H), nitrogen (N), fluorine (F), and NxHy, and various deposition methods, such as ion beam deposition, chemical vapor deposition (CVD), cathode sputtering, etc. have been studied for use as protective overcoat materials.
When used in disk-type media employed in CSS type operation, the overcoat typically protects the magnetic or MO thin-film layer at its inner diameter landing zone from damage when the data transducer head contacts the disk during a start-stop cycle, whereas, in the outer diameter data zone of the disk, the overcoat functions to protect the disk from environmental factors, such as oxidation or humidity, that can lead to corrosion and/or degradation of film properties. The tribological performance of disk-type media in CSS operation is highly dependent upon the thickness of the protective overcoat, e.g., of carbon or carbon-based material. In general, thicker carbon-based overcoats exhibit better tribological performance than thinner overcoats. However, an increase in the thickness of the overcoat results in a concomitant increase in the spacing, or flying height, of the magnetic head or other type data transducer, over the surface of the magnetic or MO medium, which, inter alia, limits the recording density and degrades performance parameters such as, for example, signal-to-noise ratio (SNR). In view of the above, and since the most tribologically critical portion of the surface area of disk-shaped magnetic and MO recording media is the CSS (i.e., head landing) zone, and the most critical portion for recording performance being the data zone, which zones have different overcoat layer thickness requirements, multi-zone protective overcoats have been proposed. One such zone design or concept utilizes a relatively thick protective overcoat (e.g., carbon-based) on the CSS zone to provide more robust tribological performance and a relatively thin carbon-based overcoat on the data zone to ensure a smaller spacing loss (e.g., SNR loss) between the transducer head and the magnetic or MO media in order to achieve better performance.
FIG. 1 shows, in cross-sectional schematic view, a magnetic recording disk 10 composed of a base or substrate 12 and incorporating a multi-zone protective overcoat 14 as described above. Disk 10 also includes an under-layer 16 formed directly on the substrate and a magnetic thin film layer 18 formed on the under-layer. Disk 10 further comprises an inner diameter CSS (or landing) zone 20, where, as described above, the transducer head contacts the disk surface during a start-stop cycle. An outer, data zone 22 extends from the outer edge 20a of the landing zone to the outer diameter 24 of substrate 12. According to the multi-zone concept, protective overcoat 14 which extends between the annular inner diameter region 20b of the CSS zone to the outer edge 22a of the data zone, has a greater thickness in the CSS zone 20 than in the data zone 22. Typically, the thickness of the overcoat 14 in the CSS zone 20 is 2-3 times the thickness of the overcoat 14 in the data zone 22. For magnetic media, the substrate 12 may comprise aluminum (A1), textured if desired and plated with a selected alloy, e.g., nickel-phosphorus (NiP), to achieve a requisite surface hardness. Alternatively, substrate 12 may comprise glass, ceramic, or glass-ceramic composite materials, similarly textured if desired. Conventionally-sized substrates for use in typical magnetic hard disk drives have outer diameters 24 of 130 mm (5.25 in.), 95 mm (3.5 in.), and 65 mm (2.5 in.), with corresponding inner diameters 26 of 40 mm (1.57 in.), 25 mm (0.98 in.), and 10 mm (0.79 in.), respectively.
Under-layer 16 is preferably comprised of sputtered chromium (Cr) or a Cr-based alloy, and the magnetic film layer 18 typically comprises a cobalt (Co)-based alloy, including binary, ternary, quaternary, and five-membered alloys. The protective overcoat 14 is comprised of a material imparting good tribological, i.e., wear-resistant, protective properties to the medium 10 and is typically composed of carbon (C), zirconium (Zr), zirconium oxide (ZrO2), silicon (Si), silicon carbide (SiC), or silicon oxide (SiO2).
Referring now to FIG. 2, shown therein, in perspective view, is a magnetic recording disk 30 having a CSS (landing) zone 36 and a data zone 40. More specifically, FIG. 2 illustrates an annularly-shaped magnetic recording disk 30 of the type having a protective overcoat thereon as shown in FIG. 1. Annularly-shaped disk 30 includes an inner diameter 32 and an outer diameter 34. Adjacent to the inner diameter 32 is an annularly-shaped, inner diameter CSS (landing) zone 36. When the disk 30 is operated in conjunction with a magnetic transducer head (not shown), the CSS zone 36 is the region where the head makes contact with the disk during start-stop cycles or other intermittent occurrences. In FIG. 2, the edge of the CSS zone 36 is indicated by line 38, which is the boundary between the landing zone 36 and a data zone 40, where magnetic information is stored in the magnetic recording layer of the disk.
As best illustrated in FIG. 1, the thickness transition of the protective overcoat 14 between the thinner and thicker data and CSS zones 22 and 20, respectively, is gradual. In practice, however, such gradual transition of protective overcoat thickness is not particularly useful or satisfactory because full advantage cannot be taken of the relatively thick protective overcoat over the CSS zone 20 providing robust tribological performance and the thinner protective overcoat providing better data recording performance within the relatively wide transition region which includes a significant portion of the width of the data zone 22.
Accordingly, there exists a need for improved means and methodology for forming, as by sputtering techniques, single- and dual-sided magnetic and/or MO information storage and read-out disks, which means and methodology provide rapid, simple, and reliable formation of multi-zone protective overcoat layers thereon with abrupt (i.e., narrow) transition zones between thinner and thicker portions respectively formed on data and CSS zones of the disks.
The present invention addresses and solves the problems attendant upon the manufacture of high recording density magnetic and MO media with multi-zone protective overcoats having highly delineated thickness variation between data recording and CSS (landing) zones, while maintaining full compatibility with all aspects of conventional automated disk manufacture technology. Further, the means and methodology provided by the present invention enjoy diverse utility in the manufacture of devices requiring thin film coatings having a gradation in thickness and properties dependent thereon, including, inter alia, optical coatings for various applications where the optical properties (e.g., optical density, reflectance, transmittance, absorptance, scattering, etc.) must be varied in a selected (e.g., radial) direction, and coatings for selectively modifying the physical and/or chemical properties of a surface in a selected (e.g., radial) direction for providing a desired property, e.g., anti-friction, corrosion prevention, hardness, roughness, etc.
An advantage of the present invention is an improved apparatus for forming on a selected portion of a substrate surface a sputtered deposit having defined inner and outer peripheries.
A further advantage of the present invention is an improved sputtering apparatus including a target assembly for forming an annularly-shaped deposited layer having sharply defined inner and outer peripheries.
A still further advantage of the present invention is an improved sputtering target assembly useful in the manufacture of disk-shaped magnetic and MO recording media.
Yet another advantage of the present invention is an improved method of sputter depositing a layer of a material on a selected portion of a substrate surface, the layer having well defined inner and outer peripheries.
Still another advantage of the present invention is an improved method of sputter depositing on a substrate surface a layer having thinner and thicker portions, with a narrow transition zone therebetween.
A yet further advantage of the present invention is an improved method for sputter depositing a multi-thickness zone protective overcoat layer on a surface of a disk-shaped magnetic or MO information storage media. Additional advantages and other features of the present invention will be set forth in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The advantages of the present invention may be realized and obtained as particularly pointed out in the appended claims.
According to one aspect of the present invention, the foregoing and other advantages are obtained in part by an apparatus for forming on a selected portion of a substrate surface a sputtered deposit having defined inner and outer peripheries, the apparatus including a target assembly comprising:
(a) a target assembly comprised of a material to be sputtered and having a planar sputtering surface including an erosion track area;
(b) a collimating shield positioned proximate to the sputtering surface and surrounding at least a portion of the erosion track area, the collimating shield comprising an inwardly facing wall defining an interior space and extending for a first length in the direction away from the erosion track area; and
(c) a blocking shield centrally positioned within the interior space and overlying a central portion of the erosion track area, the blocking shield comprising an outwardly facing wall extending for a second length in the direction away from the erosion track area and forming an open-ended channel for sputtered species between the inwardly and outwardly facing walls, the walls defining the inner and outer peripheries of the sputtered deposit, wherein:
i. the collimating shield (b) defines and limits the size of the outer periphery of the deposit and the first length thereof is sufficient to block deposition of high incident angle sputtered species; and
ii. the blocking shield (c) defines and limits the size of the inner periphery of the deposit and the second length thereof is sufficient to further block deposition of high incident angle sputtered species from the portion of the erosion track area adjacent the inwardly facing wall of the collimating shield (b).
According to particular embodiments of the present invention, the apparatus further comprises substrate mounting means (d) for positioning a substrate surface adjacent the open end of the channel; target (a) forms part of a planar magnetron cathode; the collimating shield (b) and the blocking shield (c) are circularly-shaped and concentric, whereby the open-ended channel for sputtered species is annularly-shaped.
According to further embodiments of the present invention, the target (a) further comprises an annularly-shaped erosion track area which includes a central axis extending perpendicularly thereto; the collimating shield (b) and the blocking shield (c) are coaxial with the central axis, and the collimating shield (a) surrounds the annularly-shaped erosion track at the circumference thereof; the blocking shield (c) is affixed to the erosion track area of the target sputtering surface at the central axis thereof and the second distance thereof is equal to or less than the first distance of the collimating shield (b).
According to a still further embodiment of the present invention, the substrate mounting means (d) comprises means for mounting a disk-shaped substrate adjacent the open end of the channel.
According to another aspect of the present invention, a method of sputter depositing a layer of a material on a selected portion of a surface of a substrate is provided, wherein the layer has defined inner and outer peripheries, the method comprising the sequential steps of:
(a) providing a substrate comprising a deposition surface; and
(b) sputter depositing the layer of the material on the selected portion of the deposition surface of the substrate, wherein the selective sputter depositing comprises:
i. providing a target comprised of the material and including a planar sputtering surface having an erosion track area;
ii. positioning a collimating shield proximate to the sputtering surface of the target and surrounding at least a portion of the erosion track area, the collimating shield comprising an inwardly facing wall defining an interior space and extending for a first length in the direction away from the erosion track area;
iii. centrally positioning a blocking shield within the interior space and overlying a central portion of the erosion track, the blocking shield comprising an outwardly facing wall extending for a second length in the direction away from the erosion track area and forming an open-ended channel for sputtered species between the inwardly and outwardly facing walls; and
iv. positioning the selected portion of the substrate deposition surface adjacent the open end of the channel for receiving sputtered species exiting therefrom, wherein:
the inwardly facing wall of the collimating shield defines and limits the size of the outer periphery and the first length thereof is sufficient to block deposition of high incident angle sputtered species; and
the outwardly facing wall of the blocking shield defines and limits the size of the inner periphery and the second length thereof is sufficient to further block deposition of high incident angle sputtered species from the portion of the erosion track area adjacent the inwardly facing wall of the collimating shield.
According to a particular embodiment of the present invention, step (a) comprises providing as the substrate a substrate having thereon a uniform thickness first layer of the material and constituting the deposition surface, whereby the selective depositing step (b) forms a second layer of the material, the combination of the first and second layers forming adjacent relatively thick and relatively thin portions with a narrow thickness gradient or transition zone therebetween.
According to further embodiments of the present invention, step (a) comprises providing a disk-shaped substrate and step (b) comprises providing circularly-shaped, concentric collimating and blocking shields, whereby the open-ended channel for sputtered species is annularly-shaped and the second layer of material deposited on the predetermined portion of the deposition surface of the substrate is annularly-shaped with inner and outer peripheries determined by the corresponding outwardly and inwardly facing walls of the channel.
According to still further embodiments of the present invention, step (a) comprises providing a disk-shaped substrate comprising a magnetic or magneto-optical (MO) information storage/read-out medium having inner and outer peripheries and sputter depositing the first, uniform thickness layer of the material over the entire deposition surface; and step (b) comprises selectively sputter depositing the second layer of the material over a contact start/stop (CSS) zone of the disk-shaped substrate, e.g., adjacent the inner periphery of the disk-shaped substrate.
According to specific embodiments of the present invention, steps (a) and (b) each comprise depositing a layer of a protective overcoat material for improving tribological performance of the magnetic or MO medium, wherein steps (a) and (b) each comprise sputtering a target comprising a material selected from carbon (C), zirconium (Zr), zirconium oxide (ZrO2), silicon (Si), silicon carbide (SiC), and silicon oxide (SiO2).
According to more specific embodiments of the present invention, steps (a) and (b) each comprise sputtering a target material comprising carbon (C) and depositing a layer of carbon (C) doped or chemically reacted with hydrogen (H), nitrogen (N), fluorine (F), or NxHy, the first and second layers are each about 60 xc3x85 thick, and the width of the thickness transition or gradient zone between the relatively thin and relatively thick portions of the layer of protective overcoat material is less than about 25 mils.
According to yet another aspect of the present invention, an apparatus is provided which comprises:
a sputtering target; and
means for selectively depositing material sputtered from the target onto an annularly-shaped portion of a substrate surface.
Additional advantages and features of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein only preferred. embodiments of the invention are shown and described, simply by way of illustration of the best mode contemplated for practicing the present invention. As will be described, the present invention is capable of other and different embodiments, and its several details are susceptible of modification in various obvious respects, all without departing from the spirit of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as limitative.